The Hydra2 Freehub Body replaces a worn or damaged freehub with a complete kit built around ceramic bearings for smoother, lower-friction rotation. It's compatible with Hydra2 boost and superboost hubs only, so it's a direct fit for a Hydra2-equipped wheel without adapting an older hub generation. What Our Gearhead(R) Experts Are Saying:"I pulled this freehub apart after a full wet, muddy season and the ceramic bearings still spun clean with no grit or drag. My old steel freehub would have already started grinding by that point."